Conventionally, fishfinders which perform underwater detections have been known. A common fishfinder discharges an ultrasonic wave underwater (normally, directly below) and receives a reflection wave corresponding to the ultrasonic wave. The fishfinder then analyzes the reflection wave to create data indicative of existence of a school of fish, a water depth, an underwater state, and the like (fishfinder data). The fishfinder data acquired by the fishfinder is normally displayed with a vertical axis of the depth and a horizontal axis of time.
Further, conventionally, autopilot devices which automatically guide a ship toward a preset destination have been known. Such an autopilot device, for example, detects a difference between a direction of a destination from the ship and a heading of the ship, and controls a rudder to correct the heading. Regarding such an autopilot device, a configuration in which a ship can keep circling centering on a desired location has also been known as disclosed in JP4261330B2.
When having the device guide the ship toward a location where a school of fish was detected in the past, with reference to fishfinder data acquired in the past, an operator needs to perform the following operations. Specifically, the operator first refers to a horizontal axis (time axis) of a screen image where the fishfinder data is displayed to find out a time point at which the school of fish was detected. Then, the operator operates the device to display a trace of the ship on a display unit, and estimates the location of the school of fish based on the trace and the time. The operator then instructs the device with this location as a destination of the ship. Thus, the ship can again reach the location where the school of fish was detected in the past.
However, these operations are troublesome for the operator because more than two operations are required. In addition, since in such a device the operator has to estimate the school of fish location based on the time and trace, an exact location of the school of fish, which may have been moving around, could not be identified. Therefore, an improvement has been longed for the device.